What is best to put on threads of the plug to the master brake cylinder

[GOPAPA]

I read that brake fluid does not like teflon ,,so what does that leave that will make the plug threads tight ? and one can take it back out when needed .
Please do not make this political ,,lol

[Keith Seymore]

Shouldn't need anything.

The seal is intended to take place between the flare on the end of the pipe and the corresponding seat inside the master cylinder port.


K

[GOPAPA]

Originally Posted by Keith Seymore

Shouldn't need anything.

The seal is intended to take place between the flare on the end of the pipe and the corresponding seat inside the master cylinder port.


K

I have a big nut that screws directly into the top of the ,,,,,,,,,,,master cylinder ,,must have the last thread stripped as it just keeps on turning ,, do not have a flare and pipe .

[Keith Seymore]

Pic?

[GOPAPA]

[QUOTE=GOPAPA;9197499]I read that brake fluid does not like teflon ,,so what does that leave that will make the plug threads tight ? and one can take it back out when needed .

[Keith Seymore]

Well - that was...unexpected.

I think we need to back up a few steps.

What vehicle is this?

What does that big nut do (ie, attaches the M/C to the vehicle, or holds the lid on)?

Is this part of the factory set up, or modified?

Why am I the only one participating?

At this point - I might suggest something like Permatex Aviation Form a Gasket, but might feel differently after you answer the above questions.

K

[GOPAPA]

Sorry Keith ,I guessed all knew I had a 39 chevy,, should of not thinked that,,, getting older and am selling this car ,,memory is the reason..it is a master cylinder on a stock brake set up for that year,, the big ol nut /plug is what you take out of the master cylinder to fill the master cylinder with brake fluid ..

The plug screws down the threads until the end and then just turns like the last thread is ruined ,, it has a rubber 0 ring but that does not stop fluid from oozing out when appying the brake peddle .. either I'll get a thicker 0 ring or
I will try the Permatex Aviation Form a Gasket if I feel that it will not get into the cylinder and foul up my brake system.. still open for ideas on this .

[MySons68C20]

Is the O ring captive in a groove or does it locate on the flat of the nut?
I'm thinking a thick washer and then the fatter O ring so you stay away from the stripped portion of the threads.

[chevyguyase]

It's just a cap (lid) there should be no pressure on the lid. Don't fill it to the top. when you press down on the brake pedal the fluid level will go down a little and when you let up on the pedal the fluid will return to the reservoir. The lid should just be "snugged" up. it may even have a tiny vent hole in it. Watch this YouTube video. you can go to the 23.00 min mark when he puts the top plate and cap on it.
https://youtu.be/igZgswGAvi8

[GOPAPA]

Originally Posted by chevyguyase

It's just a cap (lid) there should be no pressure on the lid. Don't fill it to the top. when you press down on the brake pedal the fluid level will go down a little and when you let up on the pedal the fluid will return to the reservoir. The lid should just be "snugged" up. it may even have a tiny vent hole in it. Watch this YouTube video. you can go to the 23.00 min mark when he puts the top plate and cap on it.
https://youtu.be/igZgswGAvi8

That is about like mine and maybe just like mine .. I did not see a rubber O ring ,,the plug looks just like mine ,, maybe the rubber O ring was already on the Plug ..my plug or cap as you call it has a hole from underneath that goes up inside the plug and then out the side of it .. if you full the cylinder to full and put the plug in,, then push the brake peddle it will pump brake fluid out the hole in the side of the plug.. I realize the hole is to let air in when you pump the brake .. good video ,, thx I will take the plug and start over and maybe use a bigger O ring or something.

[chevyguyase]

I wouldn't worry about the O-ring. Just suck out about 1/2 inch of fluid. I figure 1/2 inch because the top plate and threaded portion is probably 1/2 inch thick and you want at least 1/4 inch of air between the top plate and the fluid. I think you are putting to much fluid in it. It has to have air space in the master cylinder. No fluid should be near that lid. As long as it keeps dirt out and returns fluid splashed up while you're driving you're good to go. There is no pressure on that lid, it has to vent. Have fun my friend.

[GOPAPA]

Originally Posted by chevyguyase

I wouldn't worry about the O-ring. Just suck out about 1/2 inch of fluid. I figure 1/2 inch because the top plate and threaded portion is probably 1/2 inch thick and you want at least 1/4 inch of air between the top plate and the fluid. I think you are putting to much fluid in it. It has to have air space in the master cylinder. No fluid should be near that lid. As long as it keeps dirt out and returns fluid splashed up while you're driving you're good to go. There is no pressure on that lid, it has to vent. Have fun my friend.

Great advice ,,I learn all the time with things I hardly ever fool with..with all this good help maybe I can pass it on to another

[chevyguyase]

Glad I could help. I also try to " store up smart". I'm an old man and doing this professionally all my life. Even in the army I was a mechanic. I still learn a lot from all the talent on this site.